Cathode sputtering apparatus for the deposition of composite thin films

ABSTRACT

Cathode sputtering apparatus permitting: Simultaneously or sequentially depositing an alternate or non-alternate layer of homogeneous or heterogeneous composition on a large number or substrates without breaking the vacuum, in the course of a single cathode sputtering operation; Adjusting the distance and the orientation of centrally located targets; Disposing the substrates on an object holder rotating continuously about the targets; Carrying out the thickness monitoring measurements of the deposits outside the zones of circulation of the beams of charged particles, in the course of the deposition; Eliminating any rotating joint in the construction of the apparatus; Automating the manufacture.

May 9, 1972 R. BORGNE ETAL 3,661,760 CATHODE SPUTTERING APPARATUS FOR THE DEPOSITION OF COMPOSITE THIN FILMS 8 Sheets-Sheet 1 Filed Dec. 6, 1968 May 9, 1972 R BORGNE ETAL 3,661,760 cA'ruom: SVUTTERING APPARATUS FOR THE nEPoslTIoN OF COMPOSITE THIN FILMS Filed Deo. 6, 1968 8 Sheets-Sheet 2 f//l/A l l/ /J [I Ill lll/ll d VIIIIII 'II'.'IIA YIIIIIII I 37' s6 as gll R. BORGN 3,661,760 DE SPUTTERING APPARAT S R HE EP SITION 0F COMPOSITE HI I MS 8 Sheets-Sme?I 3 May 9, 1972 Filed Deo. 6, 1968 May 9, 1972 R. ORGNE ErAL 3,661,760

CATHODE SFUTTERI APPARATUS FOR THE DEPOSITION OF COMPOSITE THIN FILMS Filed Dec. 6, 1968 8 Sheets-Sheet 4 'w' ..1 :n lll/11111111.

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CATHODE SPUTTERING APPARATUS FOR THE DEPOSITION OF COMPOSITE THIN FILMS Filed Dec. 6, 1968 B Sheets-Sheet 5 FgS..

May 9, 1972 CATHODE OF COMPOSITE THIN FILMS Filed Dec. 6, 1968 B Sheets-Sheet 6 May 9, 1972 R. BORGNE ETAL 3,661,760

CATHoDI-z SFUTTERING APPARATUS FOR THE DEPOSITION OF COMPOSITE THIN FILMS Filed Deo. 6, 1968 8 Sheets-Sheet 7 mayo-f May 9 1972 R. BORGNE ETAL 3,661,760

CATHODE SPUTTERING APPARATUS FOR THE DEPOSITION OF COMPOSITE THIN FILMS Filed Dec. e, 1968 a sheets-sheer a 5% Z Mil w I United States Patent O 3,661,760 CATHODE SPU'ITERING APPARATUS FOR THE DEPOSITION F COMPOSITE THIN FILMS Roland Borgne, Jean Joly, and Edouard Rosiaux, Paris,

France, assignors to Societe Lignes Telegraphiques et Telephoniques, Paris, France Filed Dec. 6, 1968, Ser. No. 781,772 Int. CI. C23c 15/00 U.S. Cl. 204-298 1 Claim ABSTRACT 0F THE DISCLOSURE Cathode sputtering apparatus permitting:

Simultaneously or sequentially depositing an alternate or non-alternate layer of homogeneous or heterogeneous composition on a large number of substrates without breaking the vacuum, in the course of a single cathode sputtering operation;

Adjusting the distance and the orientation of centrally located targets;

Disposing the substrates on an object holder rotating continuously about the targets;

Carrying out the -thickness monitoring measurements of the deposits outside the zones of circulation of the beams of charged particles, in the course of the deposition;

' Eliminating any rotating joint in the construction of the apparatus;

Automating the manufacture.

PRIOR ART The present invention concerns apparatus intended for the production of microcircuits by cathode sputtering technique which is known per se. Many publications have already dealt with the production of thin films by this process. Amongst others reference can lbe made to the article by Mr. I. Pompei which appeared in lOnde Electrique, No. 453V,y December 1965 (pp. 1287 if), entitled La Pulvrisation Cathodique-Ses Mcanismes, sa Mise en Oeuvre et ses Applications vOriginales Dans le Domaine des Couches Minces, and the article by Messrs. I. W. Nickerson & R. Moseson which appeared in the revue Le Vide, November, December 1965, No. 120 (pp. 437 if), entitled Applications de la Pulvrisa-tion Basse Energie la Prparation de Couches Minoes.

BACKGROUND OF THE INVENTION The object of the present invention is to industrialise the cathode sputtering process. To this end, efforts have been made to increase the yield of the deposition step and the quality of the parts obtained, through practical arrangements perrnitting the treatment in a uniform and reproducible manner of a large number of substrates in the course of a single operation, regardless of the nature 0f said lm. The apparatus according to the present invention maybe employed to produce either homogeneous films or sandwiches of complex layers.

For this purpose, a cathode sputtering apparatus which has the following essential features has been designed and built:

Pivotally mounted and orientable multiple targets which cover a wider area than is occupied by the substrates, grouped at the centre of the apparatus and adpted to be venergised either successively or simultaneously in part or as a whole;

An arrangement of the substrates on interchangeable movable crowns carriages which surround the space occupied by the sources;

A ball bearing supporting the movable crown having a track with a V-shaped groove;

ICC

A precise resistance-measuring device for carrying out multiple tests during the operation, outside the beams of charged particles;

Electromechanical or electromagnetic systems for controlling and driving the movable members situated within the vacuum chamber;

Means for continuously rotating the substrates around the sources at a preset and adjustable uniform speed;

An arrangement of all the electrical connections and inlets in the stationary base of the apparatus.

The apparatus according to the present invention afford the following advantages over prior art designs:

The pivotal mounting and possibility of orienting the targets reduce the dispersion in thickness of the layers by increasing the concentration of the beams of the sputtered particles and the uniformity and density of these beams. The arrangement of the targets at the centre of the apparatus and of the substrates on the periphery makes it possible to design apparatus for simultaneous processing of a large number of substrates with minimum overall dimensions. The use of targets of diiferent nature makes it possible to produce films of complex composition or of the sandwich type on all the substrates treated in the course of a common operation, without breaking the vacuum. In addition to the considerable saving of time thus obtained, the quality is greatly improved, since successive depositions are carried out in the same vacuum chamber which avoids the pollution and oxidation risks encountered in dependent'operations. In the case of films of homogeneous composition, superposed deposits of layers of reduced thickness increase the homogeneity of the resulting film and hence the yield. All the substrates receive an identical deposit under equal conditions, whereby the advantage is obtained that the production is rendered more uniform. The applicants have observed that the reproducibility of the lm thickness is Within i5 The interchangeability of the movable substrate carrier enables one apparatus to receive a number of such crowns successively. This arrangement makes mass production easier, by reducing idle time. y

Adjusting, the speed of rotation of the substrates, sets up the number of runs. The idle times between the exposures of the substrates to the target beam may be utilised to allow a chemical reaction between the deposit and the atmosphere within the chamber (nitriding, oxidation, carburizing, etc.). ,j

The provision of a specially designed ball bearing track which avoids any seizure due to thermal expansion, makes it possible to actuate the movable crown with a uniform rotation.

The dynamic method of performing the tests enhances precision of the measurements up to about 3% and affords the possibility of automating the manufacture in accordance with a predetermined programme, by providing a precise electronic control apparatus for the sputtering apparatus.

Electromagnetic control and driving of the moving parts eliminates any rotating coupling or joint which, in association with the provision of all the electrical inputs and connections in the stationary base, reduces the number of possible causes of leakage.

DETAILED DESCRIPTION OF THE I'NVENTION IThe invention will be more readily understood with reference to the following description and to the accompanying figures, which are given as a non-limiting illusf tration of the invention in which:

FIG. 1 illustrates a vertical section through a rst embodiment of the apparatus along the plane A-A' of IFIG. 3.

FIG. 2 illustrates another vertical section through the same apparatus along the plane B-B' of FIG. 3.

(FIG. 3 illustrates the same apparatus in a horizontal section taken at the level of the upper face of the base.

FIG. 4 is an enlarged section of a part of the base and of ,the movable substrate carrier.

`FIG. 5 illustrates an electromagnetic system for driving the movable substrate carrier.

FIG. 6 illustrates an electromagnetic system for controlling the target shutters.

lFIG. 7 diagrammatically illustrates a possible distribu tion of the test points.

They apparatus, which is of generally cylindrical shape comprises essentially tive parts, namely a base, a central targetsupport column, a movable substrate-support crown and a 'vacuum chamber (all these parts being made of amag'netic materials), and a magnetic coil, as will hereinafter be described. They maybe mounted on a frame vsupporting the lvacuum pumps and the appropriate external electric supply sources, the latter elements only beinglmentioned here to refresh the memory.

The description, which is made, relates to an apparatus provided with only two electron sources, two targets and two target shutters. However, these values have no limiting character. Indeed, the apparatus may comprise a higher number of sources, targets and shutters. The number of such elements has been voluntarily reduced to simplify the reading of the drawings.

:The base 1 (-FIG. l) comprises an upper compartment 3 and a lower central compartment 6, which are separated by wall 4. From the bottom of the lower compartment runs the outlet 8 of the pumping duct. The lower rim of the vacuum chamber 18 presses on joint 17 tight with the upper compartment. The lower cornpartment houses two diametrally opposed electron sources 2 and 13. The lament 13 is located in an enclosure 12 opening into an orifice 11 in the wall 4 of compartment 3. The vertical wall of the lower compartment supports bushings 15 for the supply of the filaments 2 and 13. -Water inlets and outlets 16 are also provided to feed the cooling jacket 14. The base lower compartment houses the driving means for the movable substrate carrier and the control means for the retractable shutters for making the targets. The driving means for the movable carriers are better shown in ('FIG. 2). It includes an external electric motor 31 connected through a vacuum tight joint 32 to a set of gears and shafts 33 which transmits the movement to the movable crowns 83, and 70 imparts thereto a uniform and adjustable speed of rotation of 5 to 20 r.p.m. The control means for each retractable shutters 41 comprise (FIGS 1, 2 and 3) an external control button 38 and 38', a vacuum-tight joint 37 and 37 and a set of shafts and gears 3S and 35' rotating the pivot 40 and 40 in a horizontal plane and permitting individual masking and unmasking of the two targets of the apparatus.

The lower compartment of the base comprises also (FIG. 3) controllable valves such as 9 and 36 for the admission of the gases into the vessel, and also vacuumtight feed-through such as 5 and 34 for the potential and current supply leads.

In order to permit balancing of the pressures within the apparatus and a free circulation of the gases, wall 4 is formed with apertures such as those shown at 90, 91, 92, in FIG. 3. Electrical insulation is provided between the lower and upper compartments as shown in the detailed lFIG. 4, such detail are omitted from Athe general views of IFIGS. 1, 2, 3. The wall of the lower compartment 4 comprise two parts which are joined by the massive annular joint 79. The inner part of the compartment carries high voltage insulated leads rfor the targets. A

|Thewa1l 4 (FIGS. l and 2) carries the central column 19, which supports the targets 21-21 andthe shutters 41-41' (FIG. l6a) IAccess and change of the targets (FIGS. l andQ),

are easy owing to an articulated maint comprising orientable vertical supports 22 and 22 rotatablyconnected to an insulating'block 20 fast with the central columnl 'In order that the dispersion in thickness of the rlmm'ay beY reduced and excessive wear-olf of thebot'tom ofthe tare gets may be avoided, the following,arrangementsare made: the targets cover Aa lwider areafthvan Lthat of'hthe movable substrate-carrier crown both at the top and at the bottom. Each one consists of two flaps resp. 23 and 28, and 23 and 28', which are pivotally mounted on a U-shaped vspacer 25 and 25'. Correct orientation of the tlaps of the targets is obtained by turning the supports 22 and 22 around a vertical axis and pivoting theyspacers about horizontal pins 2727' and lthe flapsfatboth ends of 25.25 around pins 24-,29 and 2,4-29,..The spacing of the targets in relation to thefsubstrates/is adjusted by displacement (and further clamping) of; the spacer-flaps subassembly in the laperture of piece. 26.v Y z In order to simplify the drawings, .the electrical connections between the targets and the b iassupply connectors 5 and 34 have not been shown. For the same purpose, the shields surrounding yeach of .the .targets for elimination of backward `projection are omitted, andthe shutters 41-41' are. positioned inthe masking position. They are carried by pivots 40 and 40', which turn around a vertical axis under the control of. the shafts and gears 35 and 35,',assembly already described. Windows 39 and 39' are provided in the central column.

The position of thee-targets and the po'sitionrof-"the shields and shutters associated therewith', a't the `cen'tre' of the apparatus, is one of the'essehtial-features of Ythe invention, asv also' is the arrangement of the substrates on the inner wall of a movable carrier crown concentric with the central column?l i The movable crown is composed of two superposed cylinders 70 and 83 (FIGS. 2 and 4) which are open at both ends and are connected together as shown at 98 (FIG. 2). The upper cylinder ..70 tscnto the lower cylinder 83..Theupressure-locking Asystem `98 `provided at three points on the base o-.th'cylindersldirects the positioning of thefgupperv cylinder byf means of4 its V3 shape and ensures correct relative positioning ofi.. the two cylinders. The v,upper cylindermay be, freadilyjdisengagedby 'a simple upwardV pull. This arrangementensures rapid mounting and removal of the upper cylinder. The lower cylinder 83 is fast with the inner ring 87 of the rolling track 878877. It is driven in rotation by the driving assembly already described. `The cylinder 83 also supports on...its..outer .facecircular insulators 84 bearing conductive traoks 85, cooperatingwith the brushes 74 xed on brush holders 75, solid .withr-outer stationary ring 77 in such manner as to enslvle'electrical contact with the rotating cylinder. A vacuurnf-tight cable duct 73 extends through the vertical wall fof the-upper compartment of the base and enablesfiinterconnection of the brushes with measuring instruments situated outside the apparatus. The' substrate holders 80 inside the upper v cylinder 70" vrnaintaingthesubstrates "or the test sample such as 71 serving fori e` testing of the iilms. An electrical plug 72 is s'etinto cylinders at the level of each test sample, the female part in the upper cylinder and the male part in the vlower cylintler;- Ifhe fernaleparts of these rplugs are permanently connectedgconncfcting. to

the test samplesand ther/male parts to one of the congeneratrix or axis of thecylinder in a npmber of supi-. r-fA surface and increases the output of the depositing operations by utilising to the maximum extent the width of the beam of the particles ofthe material to be deposited. These substrate holders permit simple and rapid'reloading of the carriage crown. They consist of a slideway, secured to the wall ofy the cylinder, 'anddelimited on each side by a guide 81 having a U-shaped profile. A spring leaf 82 is lixed at each substrate location on the slideway. The substrate, which is simply slid into the guides, is pushed forward by the spring and maintained against the protruding side of the guides. All the substrates are thus situated at the same distance from the targets and in the same position.

The heating of the substrates to a temperature which may be chosen between 250 and 400 C.`is effected by means of infrared radiation sources mounted on supports fixed on the wall 4. One of them, 93, is shown in FIG. 4. However, this heating method has no limiting character, and any'appropriate method may be employed without modifying the nature of the invention.'

'I'he expansions produced by the high temperature of the substrates-during operation, andthe impossibility of employing any lubricant inside the vacuum chamber, have led the applicants to design a special 'rolling track 87-77 for the movable substrate carriage, which is illustrated in detail in FIG. 4. The stainless steel balls 88 of the bearing are disposed between two beryllium-bronze rings 87 and 77. The ring 87, which issecured to the base of the substrate carriage, is formed with a semicircular groove in which the balls are lodged. The stationary ring 77 is machined with a V-shaped 'groove forming two Yplanar slopes 76 and 78. The balls on the surface of the lower slope 78 and the point contact will be displaced on the slope as a function of the expansion. The clearance provided between the upper slope 76 and the balls 88 is sufficient to prevent any interference with the displacement of the balls, while preventing them from leaving the track.

Disposed over all the members just mentioned is the vacuum chamber 18, which lits into the joint '17 ofthe base. The said chamber (FIGS. 1 and 2) comprises at its upper end an electrical bushing 94 supporting the anode 95, which is common to all the electron beams of the apparatus, and the bias voltage supplied by an external source is applied therethrough. In another version of the apparatus, the vacuum chamber is of hemispherical form and has no bushing. This arrangement favours the vacuum-tightness of the apparatus and reduces the fragility of the chamber. In this second version, the anode common to the electron beams is supported by a rod secured to the centre of the central column and is fed by means of a bushing provided in the lower compartment of the base.

In another version of the apparatus (FIGS. 5 and 6), the joints 32 and 38 are omitted. Electromagnetic devices are employed to control the movable members situated within the vacuum chamber. The substrate carrier (FIG. 5), drive 33 is actuated by a permanent magnet 50 which is arranged to rotate around the horizontal axis. A driving plate 52 provided with solenoids 51 and rotated by the adjustable speed motor 31 is situated outside the apparatus. Coils 51 are supplied with direct current through a system of brushes contacting circular tracks 53. This mode of drive, apart from the advantages which it alords in regard to vacuum-tightness, ensures a flexible coupling between the motor and the substrate carrier, whereby the transmission of any vibrations from the motor to the substrates is obviated. The control of the retractable shutters (FIG. 6), is also an electromagnetic. FIG. 6a shows by way of example a plan view of 'the central column 19, above which are mounted two targets Z0 and 20' provided with shields 60 and 60'. The shutters 41 and 41 are mounted on horizontal support arms 61 and 61' secured to the upper end of vertical shafts 62 and 62 which extend into the lower compartment of the base (FIG. 6b)

vafter having passed through the wall 4 through bearings v63 and 63'. They are provided at their lower end with an arm 64 and 64' forming a lever terminated by curved permanent magnets 65 and 65', the levers and the magnets being situated in a common plane "perpendicular to the verticalfshaft. The permanent magnets 65 and 65 are freely movable Awithin coils 66 and 66. It is merely necessary to'apply a unidirectional voltage to the latter to obtain the vdisplacement of the magnet and consequently that of the shutter. The movement of the magnets and thereforethat of the shutter may be controlled by reversal of the direction of the current in the coils. All the electrical connections between the reversing switches situated outside the chamber and the solenoids may be effected by the provision of a single vacuum-tight bushing in the lower compartment of the base. This apparatus has advantages iu regardfto vacuum-tightness and in addition is less cumbersome and easier to construct than the purely mechanical system in case of apparatus comprising a large number of targets.

vThe equipment of the apparatus is completed by an external magnetic coil 96 (FIG.1), around the vacuum chamber. The magnetic coil concentrates the plasma. The electricl and pressure-measuring instruments are not shown in the figures.

' The operation of the apparatus according to the invention does not differ essentially from that of similar cathode projection apparatus well known to the person skilled in the art. However, this apparatus affords novel possibilities of use owing to the mechanical features adopted therein.

After the completion of a primary exhaustion, followed by a secondary exhaustion, the substrates are heated for about one'hour at the appropriate temperature. When the discharge has been set up, the substrates are set in rotation. The targets are cleaned by projection onto the shutters. The operations which then follow depend upon the nature and the complexity'of the deposition which it is desired to perform. For example, if the deposition is to comprise two superposed layers of different natures and of given thickness, the procedure is the following. The target which is to supply the first deposit is first unmasked and the thickness of the deposit is monitored by measuring the resistance of the test sample each time it travels past the measuring station. When the required resistance has reached the desired Value, the ap is closed again, the target voltage is cut oi and the heating of the cathode is stopped. The second projection, which is of different nature, may then be eiected with the aid of a second target and monitored in the same way.

Various modifications may be made to the apparatus, both in regard to the nature of the successive deposits, which vary, and to their constitution. By adopting appropriate means such as those illustrated in the diagram of FIG. 7, it is possible to monitor the performance of complex operations during operation (in-line testing). The number of measuring stations may be multiplied by appropriately distributing them around the substrate carrier. In an apparatus comprising three targets C1, C2 and C3, for example, each test sample t1, t2, t3 on the substrate carrier is connected to the female part of a connecting plug. The conductive tracks (FIG. 4) are divided into as many electrically insulated sectors p1, p2, p3 as there are test samples. Each track sector is in turn connected to the lower cylinder on the substrate carrier to the male part of a connecting plug. Under these conditions, locking` of the upper cylinder establishes the connections between each test sample, such as t1, and a track sector such as p1. The brush holders b1, b2, b3 are also distributed around the upper compartment of the base and shifted in relation to one another by an angle equal to that formed by the directions f1, f2, f3 of two consecutive beams of particles. The tests are made at the time when the test samples reach the vertical of the brushes. The measurement made at a station, for example b1, monitors the deposit produced bythe target precedingiit, for example c1, on the substratesngl.:V .t v ,r Y ,Y t, .k l A After depositions, the substrates are allowed to cool and, after the exhaust equipment has been disconnected, the pressure inthe chamberissfrestored:tolatmospheric pressurerby-adrnitting ultra-pureqargon, A further depositing operation -vcan then `be vlundertaken without interruption on further substrates, simply by replacing the substrate carrier-carrying .the processed substrates by another, previously loaded carrier.v l i v t Allgthe operations involved in `carryingouttheactual sputtering may beautomated. InI thistype of production:lv As a function of pressure and of time the primary and secondary exhausting operations, the heating of the sub- 1`.l An apparatus yfor successive oralter'nate deposition ff,

o'fithin hnsl of different materials `on a plurality of sub-` strates by sputtering in the same batch operation and for semicontinuous monitoring of the thickness of thelsputtered films comprising: j (y (a) a cylindrical vertically'arranged vacuum chamber; (b) a stationary base member; t (c) a gas tight joint mounting said chamber on said base; (d) an apertured plate dividing said base member into upper and lower compartments; (e) a centrally located column extending upwardly into said chamber from said base; w (f) at least one pair of quadrangular targets; (g) articulated means on the upper end of said column for adjustably supporting said targets with respect to each other and with respect to said column; (h) at least one movable shutter;

40 20L-192 y i y 7^ t *u 3 wir v (i) means controllable from the exterior of said apparatus andextendng through lsaidcolumntforV adjustably positioning said shutter with respect to said targets; (j) means for removably supporting in rows and columns a plurality of substrates to be coated including a cylindrical-carriennierber positioned concentrically around said targets; (k) means to'rotate said 'cylindrical carrier; l '(1)' electron guns in said base for supplying electron beams to` thevannularspace between said targetsand l i saidr carrier memberthrough, apertures in Y.said plate; (m) means said base affording' connection of a source of gas to the interior ofV said apparatus; (n) further means in said base affordingconnectioil of a vacuum pumpttothe interior` of said apparatus; (o) an anode located in the uppermost part of said chamben" t, v (p) a focusing coil surrounding said chamber; l y, (q) means on said stationary base electrically 4inter: connecting with saidrotatable carrier member; ,r (r) and monitoring meansvconnected to said last ,motif tioned means to measure the resistance Lof the depos: ,ited film on said substrates at a time when said 'subl strates are rotated by said carrier member to positions substantially diametrically opposite said targets to yield a reading proportional r-to the thickness of the deposited iilm.

v References Cited 3/ 1970 Wehneret al -..-204-298 HOWARD S. WILLIAMS! Primary Examiner N. A. fKAPLAN, Assistant Examiner z U.s. c1. XR.' Y 

